Loudspeaker cone diaphragm and method of producing same



D. H. CUNNINGHAM Feb. 11, 1936.

LOUDSPEAKER CONE DIAPHRAGM AND METHOD OF PRODUCING SAME Filed Jan. 31, 1934 v INVENTOR:

David H Cunn ingham Patented Feb. 1 l, 1936 PATENT A OFFICE LOUDSPEAKER CONE DIAPHRAGM AND METHOD OF PRODUCING SAME David H. Cunningham, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 31, 1934, Serial No. 709,111

12 Claims.

This invention relates to loudspeaker diaphragms and the method of producing same, and in particular it is directed to the object of producing such a diaphragm as will have certain advantages of flexibility around its peripheral portion while having the desired stiffness at other portions.

Heretofore, in the manufacture of loudspeakers,

it has been customary to secure the conical portion of the diaphragm to a' supporting ring by means of a flexible element which is not integral with the cone itself. The process of assembly is not only costly but the structure does not always lend itself to good performance of the cone.

I have found that when the thickness of the material of which the diaphragm member is blanked out is reduced adjacent the peripheral portion to give it the desired flexibility, it is possibie to select a cone material of suitable thickness and stiffness to exhibit the optimum of vibratory characteristics of the cone itself.

I am aware of attemps that have been made in the past to produce a conical diaphragm for a loudspeaker by the adoption of various more or less elaborate processes in the making of the paper itself from which the cone is ultimately formed. Thus it has been proposed to build up the structure beginning with the paper making operation which consists in depositing the paper pulp upon a screen having a conical contour. The flow of pulp would in that case be controlled so as to deposit upon the screen a greater thickness of fibers near the center of the cone than at the periphery. Hence, when the cone was finished, it would have the desired stiffness in the center portion and would perhaps have the desired flexibility around the rim. This process appears to be disadvantageous in that it is quite expensive and the product itself cannot easily be held uniform and within reasonable tolerances.

Accordingly, I have adopted a method which has decided advantages in that it makes possible the selection of a suitable cone material from a wide range of available kinds of paper or other sheets. Furthermore, the grinding operation to which the blanks may be subjected can be per formed at low cost compared with the cost of cementing an auxiliary flexible rim strip around the cone blank. I

Cone diaphragms made according to my preferred method are of improved appearance because there is no use of cement and no showing of cement about the rm. Furthermore. there is complete freedom from defective operation of the cone in such instances as are caused by failure of the cement to bond together the cone and the rim piece along any part of the seams.

It will be seen from the above that my invention has for its object to provide, as an article of manufacture, a sheet of fibrous material from 5 which loudspeaker diaphragms may be suitably formed.

A further object of my invention is to develop a process by which flat material can be utilized to form a cone diaphragm of sufficient stifiness to 10 give it satisfactory vibratory characteristics, while having a rim portion, integral therewith, which has suitable flexibility.

My invention is defined according to the scope of the appended claims. The carrying out of 5 the process and the nature of the article produced may best be understood. however, by reference to the specification following, when read in connection with the accompanying drawing, in which: 90

Fig. l is a side view. partly in section, of a typical cone diaphragm;

Fig. 2 is a plan view showing a blank made from flat sheet material and having a portion near the c rcumference reduced in thickness;

Fig. 3 is an enlarged cross-sectional view along the line 3--3 of Fig. 2; and

Fig.4 is an enlargement of that portion of the diaphragm which is also shown sectionally in Fig. 1.

Referrin now to the drawing in detail, I show a truncated cone diaphragm I having an orifice 2 at its center and having corrugations 3 formed about the rim. This cone is preferably made from 36 a blank as shown in Fig. 2. In order to give it conical shape. a sector is cut out so that the two edges 4 may be brought together and lapped one over the other.

Before cementing the edges 4 together, I resort to a process of reducing the thickness of. the blank near its periphery. This operation is performed preferably by placing the blank and holding it in a hat position on a tum-table and rotating it beneath a grinding wheel. If desired, 45 a weight can be placed on top the paper to keep it flat. The tum-table is so spaced from the grinding wheel that, when it is rotated, some of the fibrous material from the blank is removed from the rim area shown at 5 in Figs. 2 and 3. It is preferable that the axes of rotation of the grinding wheel and of the turn-table should intersect. It will be understood that the apparatus required for performing this operation can be very simple in design and yet provided with suit- 55 able adjustments for gauging the depth of the grinding operation as applied to the zone 5.

As compared with other processes the grinding operation as just described may be performed on successive blanks at low cost. The process lends itself to uniformity of product. The sound reproducing qualities of the diaphragm are enhanoed.

Fig. 3 shows how, in the grinding operation, the thickness of the material throughout the zone 5 may be reduced, if desired, to substantially half the original thickness of the paper. This relation between the original thickness and the reduced thickness need not be adhered to, however, if the requirements for a satisfactory finished article appear to dictate grinding oif more or less than half the thickness.

ZI'he operations of molstening and molding the cone to form circular corrugations adjacent the periphery are well known in the art. By including these operations, however, as steps of my process, novelty is imputed to the results obtained by virtue of the increased flexibility of the rim portion when it is both thinned and corrugated.

Although I have described a specific embodiment of my invention as an article of manufacture and have illustrated its manufacture by specific steps of a process, it will be understood that the foregoing specification is merely an example of how my invention may be carried out. To those familiar with the art, various modifications of the article itself and of the process of producing it will readily suggest themselves. For example, it may be found that a portion of the disc can be sand-blasted, scraped, milled or otherwise treated as by softening, stretching, and molding to give it suitable flexibility, and preferably to reduce the thickness adjacent the rim. Such modifications would not, however, be a departure from the spirit and scope of the invention as defined in the appended claims.

I claim as my invention:

1. As an article of manufacture, a circular sheet of fibrous material from which a sector has been cut away and from an annular surface near the periphery of which a substantial portion of the thickness has been removed.

2. In a membranous device for use in a loudspeaker, a sheet of fibrous material conicaily formed and having near its periphery a zone the thickness of which has been substantially reduced by abrasion.

3. A conical loudspeaker diaphragm made from a fibrous flat blank and having a zone thereof finished to a fractional part of its original thickness.

4. A loudspeaker diaphragm formed from a fiat sheet of fibrous material a portion of which adjacent the periphery has been reduced in thickness and then corrugated so as to effectively increase its flexibility per unit of area.

5. A loudspeaker diaphragm formed from a sheet of fibrous material from a portion of which some of the original fibers have been removed.

6. The method of producing a loudspeaker diaphragm which consists in cutting a blank from a fibrous sheet, turning the blank on its center, grinding 01! some of the fibers near the periphery of said blank and forming said blank conically and with circumferential corrugations.

7. The method as defined in claim 6 further characterized in that the fibrous structure. is

moistened and molded under heat and pressure'to give it the desired configuration.

8. The method of producing a diaphragm for a sound propagating device which consists in blanking out said diaphragm from sheet material having a fibrous structure, swiveling said blank on its center, grinding said blank near the periphery thereof to reduce its thickness at that portion, and moistening and molding said blank into conical shape with circumferential corrugations disposed along the portion of reduced thickness.

9. The method of producing a diaphragm for a sound propagating device which consists in blanking out said diaphragm from sheet material, rotating said blank about its center while subjecting a portion of its surface to abrasive action whereby said portion is reduced in thickness, and

forming said blank into a finished article having the desired configuration.

10. The method as defined in claim 9 further characterized in that the operation of reducing the thickness is applied to a zone which is at least coextensive with the formation of circumferential corrugations in the diaphragm.

11. The method of preparing a diaphragm for use in a sound propagat ng device which includes the steps of cutting a fiat blank from a fibrous sheet, reducing the thickness of the blank near its periphery, and molding said blank with circumferential corrugations.

12. As an article of manufacture, a circular sheet of fibrous material from which a sector has been cut away and from an annular surface near the periphery of which a substantial portion of the thickness has been removed. said sheet having then been formed into a conical diaphragm having corrugations in said annular surface.

DAVID H. CUNNINGHAM. 

